The present invention relates to a foamable silicone rubber composition.
Silicone rubber foams are light and offer an excellent heat resistance and weather resistance. Based on these properties, silicone rubber foams have entered into wide use, most importantly in the automobile parts sector. Silicone rubber foams are specifically used as various types of seals, packings, gaskets, O-rings, and so forth.
Methods for the preparation of these silicone rubber foams include (i) the addition of a thermally decomposable blowing agent to a thermosetting silicone rubber composition and (ii) the utilization of hydrogen generated as a curing by-product. A problem with the former method (addition of thermally decomposable blowing agent) is the toxicity and odor of the associated decomposition gas. Another problem with the former method is inhibition of the cure by the blowing agent when a platinum catalyst is used as the curing catalyst. Problems with the latter method (utilization of hydrogen generated as a curing by-product) are the explosive nature of hydrogen and the caution that must be exercised in handling during storage of the uncured mass. A further problem with both methods is that the cells in the silicone rubber foams produced by them are large and nonuniform. These methods essentially cannot give silicone rubber foams that have uniform, microscopic cells.
The present inventors carried out investigations directed at solving the aforementioned problems. They discovered as a result that the addition of specific hollow plastic microparticles to a liquid silicone rubber composition makes possible the production of a silicone rubber foam having uniform microcells without the generation of hydrogen or toxic gases during the foaming process. The present invention was achieved based on this finding.